J.P. Morgan is on its way to becoming the fourth of 18 banks to settle two-year-old lawsuits by the regulator in charge of U.S. mortgage giants Fannie Mae and Freddie Mac over mortgage-backed securities.

Fannie and Freddie have booked “substantial losses” on those securities and blame the banks for false declarations about the underlying health of those mortgages.

The suits against the 18 banks, nearly all identical and 17 of them filed together on the Friday before Labor Day weekend in 2011, claim that figures investors use to judge the credit worthiness and potential safety of a mortgage-backed security were inflated.

The banks have largely rejected the claims of the lawsuits, which in total seek reparations for more than $200 billion in mortgage-backed securities. The general argument was Fannie and Freddie knew the mortgage market as well as anyone and should have known the investments were liable to blow up.

But J.P. Morgan would be the fourth to settle a suit, following General Electric, Citigroup and UBS. Citi was sued over $3.5 billion in securities; GE Capital had sold $549 million; and UBS had a total of $6.3 billion in exposure. GE and Citi didn’t disclosethe size of their settlements, while UBS said it was paying $885 million.

J.P. Morgan’s settlement would work out to about 12% of the $33 billion in securities that the bank sold to Fannie and Freddie. UBS’s payment was about 14%.

Fannie and Freddie shares are both up more than 11% this week on talk more big payouts could be coming. Analysts are using a 13% rate to handicap how much the remaining banks would owe, admittedly a simplistic formulation as the quality of loans at each bank would have been different. Meanwhile, for bank investors, the banks have likely reserved for losses already. But the potential numbers are big.

Goldman Sachs and Morgan Stanley would both be facing around $1.4 billion in settlements, using the 13% model. Ally Financial would be looking at around $780 million and First Horizon National would be up against about $115 million. (Wells Fargo said the estimate for First Horizon’s would be about 32 cents per share for the bank, which would reduce the estimate the analyst had for 2013 EPS by 44%.)

In Europe, the concern of big payouts hit some bank shares this week, particularly Royal Bank of Scotland, which has $30.4 billion in exposure. Analysts estimated it could face a nearly $4 billion settlement. Nomura said the litigation would be an overhang over the stock, adding it believes the average delinquency rate is among the highest for RBS’s loans.

RBS shares dropped 5.3% on Monday after J.P. Morgan’s amount was first reported, though are back up 2.5% Tuesday.

Among other big global banks, using the 13% model would mean Credit Suisse and Deutsche Bank both face around $1.8 billion in potential settlements while Barclays would be up against $637 million. HSBC would face over $800 million, Nomura would be looking at $260 million and Societe Generale could potentially have a $169 million payment on its hands.